The invention relates to a magnet system for a valve as defined herein.
In magnet valves, a free-floating armature coupled with a valve body has an the advantage which does include a mass to be moved for the bearing guides, it has a higher natural frequency because of a more-compact structure, and hence it has better hydraulic damping upon impact, with less wear. A compact structure reduces the wobble of the armature and minimizes hydraulic oscillations and errors in linearity. Problems of fuel delivery through the bearings disappear. Bearing jamming is eliminated and costs are reduced. A free-floating armature, because of greater orbital tolerances, necessarily minimizes both interference forces and the masses to be moved.
There are already magnet valves in which the permanent magnet is embodied as a plate and the magnetic lines of force of the permanent magnet run in the same direction as the coil of the electromagnet, and in which the armature is embodied as a valve body and opens in the direction of the lower-pressure side; such a valve is described in German Offenlegungsschrift 3 237 532. However, at higher voltage and with switching of the end stage of the electronics, the attraction of the armature cannot be prevented. It has therefore already been proposed that a second permanent magnet be provided. In another known device, namely a camera shutter described in U.S. Pat. No. 4,240,055, although the requirements for low mass, high magnetic efficiency, low magnet conductor cross sections, stable axial position and calibratability can be met, nevertheless a reversal of the magnetic field when there is a variable feed voltage cannot be systematically prevented. Furthermore, because of a three-piece armature, this camera shutter is expensive, and the non-circularly symmetrical arrangement causes manufacturing tolerances with undesirable interference forces. Also, attraction at elevated voltage cannot be prevented very well.